Without limiting the scope of the invention, its background is described in connection with the development of biological materials (biomaterials, hereafter) by incorporating polymers with organic or biologic substituents (bi-functional biomaterials, hereafter). A nucleotide and/or amino acid sequence listing is incorporated by reference of the material on computer readable form.
Heretofore, in this field, the means of developing biologic materials has taken a variety of approaches, wherein traditionally non-biologic (i.e., non-organic) materials are modified in one or more ways to present biologic features that resemble or are recognized by natural biologic tissue (i.e., organ tissue). Modifications have included the use of protein adsorption and self assembly, synthesis of novel graft-copolymers with the desired functional groups, and direct covalent surface modifications. Ultimately, the goal of manufacturing such biologic materials is to create a biomaterial that is flexible enough to adapt to changes in molecular design, is easy to synthesize, and can be applied to many different biologic uses (e.g., claudication, implantation, transplantation, biologic regeneration, growth, and as biologic replacements, modifications, or substitutions).
Recent investigations into creating biologic materials include the use of a microfabrication technique. Here, proteins and other molecular structures (including cells and/or tissue) are attached to the surface of a material that exhibits biologic properties (e.g., binds to one ore more biologic or organic compounds); the attachment is generally through nonspecific or specific recognition of the protein or other molecular structures to the material. For example, microcontact printing with a PDMS stamp is used to create micropatterns on the surface of a material. In the second stage, proteins or other molecular structures are adsorbed to the solid surface of the material. The unfortunate consequence of using such a technique is that the adsorption is nonuniform and creates irregular surfaces, much of which does not exhibit the necessary biologic properties that were initially desired. This is because the process is largely dependent upon non-specific interactions between the molecular structure and the material surface and these non-specific interactions result in less than optimal surfaces with randomly oriented molecules.
Others have engineered polymer surfaces to a material, using engineered polymers that may even control the adhesion of molecular structures to the polymer surface and are thought to be able to be used to attract one or more cells to the surface while maintaining the phenotypic expression of the cells. The drawback is that few polymers really have suitable functional groups that are able to covalently attach to a biologic structure. This fundamental flaw limits the use of a polymer as a biologic surface unless it is also modified to become more attractive to one or more biologic structures (e.g., organic compounds, biologic compounds, cells, tissue, etc.). Common approaches to functionally modifying a polymer include introducing reactive groups (e.g., poly(L-lysine)) at existing polymer surfaces by incorporating monomer units into the polymer backbone. Such approaches, however, are cost prohibitive by requiring complicated synthetic pathways and do not create uniform biomaterial surfaces (i.e., a surface containing one or more biologic structure).
An alternative method is a silanization technique that immobilizes peptides on the surface of a material. The method was demonstrated by depositing a silane film with terminal functional groups on a titanium oxide surface. In addition, the resulting surface could be further modified with different bi-functional linkers, eventually leading to the covalent attachment of a peptide sequence such as Arg-Gly-Asp (RGD)—a cellular recognition sequence used by several biologic proteins. The technique was also altered using different silane-like compounds such as aminosilane. Accordingly, a number of reactions with bi-functional linkers were performed, including: (a) glutaraldehyde to yield a linkage between the aldehyde imine and the peptide amine; and (b) aminosilane with a mixture of peptides and carbodiimides to yield a linkage between the amide and peptide carboxyl groups. These reactions were limited, however, in their ability to create specific peptide attachments at one or more defined sites. Consequently, unordered and nonuniform surfaces are produced.
Subsequent surface modification techniques have been used to create biologic materials with specific binding surfaces. For example, one technique was developed to create a neural surface (e.g., similar to the extracellular matrix of nervous tissue) using a polymer coupled to peptides. Here, poly(tetrafluroethylene-co-hexafluoropropylene) was reduced with sodium naphthalide to introduce carbon-carbon double bonds at the surface (e.g., a carbon-like film) and the reduced surface was then further modified to introduce hydroxyl groups (e.g., with hydroboration/oxidation) or carboxylic acid groups (e.g., through oxidation). The polymer, thus, contains either a hydroxyl (—CHxOH) or carboxylic acid (—COOH) surface that could be coupled to one or more peptides. In fact, the attachment of 5- and 6-mer peptides was found to promote neurite extension (i.e., modified growth).
Materials with surfaces that resist protein adsorption and fouling have also been developed. These materials may be further modified with biologic components to promote specific molecular and/or cellular interactions. Polymers such as poly(ethylene glycol) or PEG that resist protein binding are suitable to use for these modifications. In addition, peptides such as those containing RGD sequences (e.g., acrylamidoyl peptides) may be incorporated into mixtures of PEG diacrylate to create a peptide-modified polymer. Unfortunately, this technique is unable to control the spatial orientation of peptides on the material (i.e., polymer) surface and only works with biologic structures of limited type and size. This type of modification is limited to polymers that have the ability for Pegylation, which can be important for immobilization of peptide via covalent reactions.
As evidenced by the above, current techniques are unable to create biologic materials with functional surfaces, that is surfaces that displays properties that allow for and promote interactions between the surface and another biologic structure (e.g., nucleic acid, protein, cell, tissue, organ, chromophore, etc.). There is a need, therefore, to develop such a technique that is both cost-effective and adaptable to one or more biologic structures to enable its widespread application.